The present invention relates to a fastener provided with a washer, and a method of fastening with the use of the water.
It is known to fasten objects with one another with a fastener which has a multi-part replacement nut, for example including an inner sleeve, an outer sleeve, and a washer. Such a replacement nut is disclosed for example in our U.S. Pat. No. 5,341,560. Another replacement nut is disclosed in our U.S. Pat. No. 6,254,323 in which a bolt has a spline underneath its upper thread, to which a washer is non-rotatably connected, and the bolt also has engaging means for applying a reaction force, while an active force of the same tool turns the nut on the bolt thread and the washer face. In the fastener disclosed in both above mentioned patents, the common features are the use of the action and reaction force of one tool, the elimination of reaction arms on torque power tools, the conversion of torque to torsion-free bolt stretching and obtaining for the first time the desired residual bolt load as compared to torque, which is estimated based on calculated frictions rather than actual frictions or hydraulic tension, which is based on estimated bolt relaxation when the force is transmitted from the elongated bolt to the hand-tight nut.
The problem found in the industry with the fastener disclosed in U.S. Pat. No. 5,341,560 is that, since the nut has to be made with two sleeves whose outside diameter has to meet the outside diameter of a regular nut, both sleeves have less material than a regular nut. This requires the use of high strength materials, which causes a reluctance on the part of the customers to change materials and fear of the unknown. In the fastener disclosed in U.S. Pat. No. 6,254,323 the bolt needs to be altered, which is not just costly but not easily acceptable by the industry. In other words the fastener disclosed in our U.S. Pat. No. 5,341,560 requires alteration of the nut, while the fastener disclosed in our U.S. Pat. No. 6,254,323 requires alteration of the bolt. In addition, both versions are expensive to produce, adding to customer""s reluctance to purchase these fasteners.
Accordingly, it is an object of the present invention to provide a fastener provided with a washer, and a method of fastening with the use of the washer, which avoid the disadvantages of the prior art.
In accordance with the invention, one feature of present invention resides in a threaded fastener for connecting at least two parts which constitute an object, which fastener has a bolt having a thread; a nut screwable on the bolt; and a washer to be applied between a nut and an object and having a body with an axis and with a first bearing face surface located at one axial side and adapted to cooperate with a nut, a second bearing face surface located at an opposite axial side and adapted to cooperate with an object, and at least one third turning resistance surface adapted to cooperate with a thread of the bolt, so that when the nut is turned with a given force in one direction and the body of the washer receives simultaneously said given force in an opposite direction, only the nut turns to tighten or loosen the bolt and the body of the washer remains rotation stationary, while the bolt elongates or relaxes in an axial direction.
Still another feature of the present invention resides in a method of assembling at least two parts with one another, comprising the steps of introducing a bolt having a thread into the at least two parts so that a free end of the bolt extends outwardly beyond at least one side of the two parts; placing a friction washer on said free end portion of said bolt so that said friction washer engages with said thread of said bolt to create a turning friction between said washer and said bolt and so as to abut against said at least one side of the at least two parts; threadably connecting a nut to said free end portion of said bolt so as to abut against the friction washer and to form an assembly; placing a torque power tool on the assembly so as to tighten or loosen the nut with a turning portion of said torque power tool connected to the nut to overcome a threaded friction between the bolt and a facial friction with the friction washer to turn the nut, and with a reaction portion of the torque power tool connected to the washer to absorb a reaction force due to a facial friction of the friction washer with the nut, a facial friction of the washer with said at least one side of the two parts and a turning friction of the washer with the bolt selected so that the washer remains stationary while the bolt elongates or relaxes in an axial direction.
When the fastener is designed in accordance with the present invention and the method is performed in accordance with the present invention, regular nuts and regular bolts can be used. In other words the customer can use whatever he has adding merely a washer. The benefit is quite remarkable. First of all the product is much less expensive than each of the products in the above mentioned patents. Secondly, the customer uses his approved bolts and nuts. Third, instead of reacting on a part of the nut directly as in the U.S. Pat. No. 5,341,560 or indirectly as in the U.S. Pat. No. 5,946,789 by passing the reaction force through the washer to a part of the nut, the reaction force is solely absorbed by the washer. Furthermore, the solution proposed in the present application provides the identical benefits as the solutions disclosed in the above mentioned patents, one of which is a torsion-free elongation of the free portion of the bolt, a known coefficient or friction between the nut face and the washer face and thus a known bolt load precision, a reaction-arm free hydraulic torque tool use, a bridge-and precision puller-free bolt stretching. In other words, torque is converted into torsion- and side-load-free bolt elongation to the desired bolt load by means of a torque power tool, which can be also applied to torque regular nuts with a reaction member. It needs to be considered that most bolts in the industry are through bolts with a nut on the other side or blind bolts threaded in the bottom part of the two parts.
It is known that if a torque power tool is applied to a fastener in a way where the nut is turned by the active force of the torque power tool and the reaction is absorbed by a regular washer underneath the nut, then either the nut or the washer will turn at will or the bolt turns along with the nut and nothing is accomplished, or the bolt end tightens further into the blind hole causing the bottom threads to mushroom which makes disassembly extremely difficult. The reason for that is that the nut has two friction areas, the threaded connection with the bolt which creates a drag friction and the facial area with the washer, whereby the washer has one facial area with the nut and one facial area with the two parts to be assembled. In other words, both have two friction areas. While it is correct that a threaded friction is a little less than a facial friction, the difference is minute as the facial friction between the washer and the nut balance each other out, so that there is merely one minute difference between the nut and the washer. At the same time if the bolt is a through bolt, the thread friction between the bolt and the nut is such that the bolt turning resistance is much less than the facial friction of the washer and while the washer would absorb the reaction force without turning, the bolt would turn along with the nut and nothing is accomplished unless a back-up wrench is used to stop the bottom nut from turning. Therefore, neither is enough to guarantee that only the nut turns, which is why the third friction area had to be introduced to the washer.
On the other hand, if the washer is connected with the thread of the bolt, the bolt can not turn along with the nut because the washer will have to lift up which it can not because the nut is on top of it. Bolt elongation resulting from turning down the nut is, therefore, impossible. The present invention therefore provides a bolt thread engaging washer section which is connected with the bolt thread. This alone would not help because this section could move either along with the bolt by rotating or upward if the bolt rotates in it and nothing is accomplished. This in turn would allow the bolt to turn along with the nut as the section rotates or moves up. Therefore in accordance with a further new feature of the present invention, the bolt thread engaging means is frictionally connected with the body of the washer, so that its rotational or upward movement is subject to overcoming a friction greater than a drag friction created on the bolt by the turning nut, to stop the bolt from turning. This friction in conjunction with the two facial frictions of the washer assure that the bolt does not move along with the nut, that the bolt is stretched, and that the washer and its bolt thread engaging section do not rotate while the nut is being turned.
If the reaction force of the tool is applied to the outside of the washer through engagement means thereon, it is also possible to have a pin or the like connected at one end to the thread engagement section and having its other end sticking out of the circumference of the washer so that when the tool is connected with the washer the pin is pushed inwardly pushing the thread engagement section inwardly into the bolt thread.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.